Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2007
Publication Date: N/A
Technical Abstract: Use of aerially-acquired canopy-to-air temperature differences (CATD) for crop water management in humid subtropical climates has been demonstrated to be especially problematic. The small differences in canopy-to-air temperature that occur when the crop begins to show signs of stress are difficult to detect due to the prevailing low vapor pressure deficit (VPD) which negatively impacts crop evapotranspiration, and the high-frequency occurrence of transient cloud cover which complicates the accuracy of field-scale CATDs. Images of an irrigated cotton field were acquired from an agricultural aircraft equipped with an Electrophysics PV320T thermal imaging camera having 12-bit image resolution. The objectives of this investigation were three-fold: (1) quantitatively and qualitatively assess areas of heat/water stress in a cotton field with sharp contrasts in soils; (2) evaluate spatiotemporal relationships among the thermal infrared images obtained from July-September 2006; and (3) compare these patterns of thermal zonation with mid- to late-season crop development and yield using spatial statistics. In one component of the study, each thermal image in the time-series was re-sampled to 8-bit resolution and then composited to produce a cumulative thermal image that spanned close to five weeks of elapsed time. Geostatistical analysis (i.e., using Local Moran’s I Spatial Autocorrelation or LISA) of this cumulative thermal map highlighted two distinctive zones of the field where assemblages of high crop-soil temperature values were significant and areas characterized by substantially cooler canopy temperatures. A bivariate LISA map revealed the tightly-coupled linkages of low yield zones with areas of the field subjected to the highest temperatures (P ' 0.01) and significant complementary associations of high yield areas with lower canopy temperatures (P ' 0.01). In addition, ground-truthing combined with the use of both color infrared and thermal imagery series demonstrated that canopy closure did not occur in the most heat/water-stressed portions of the field, and from mid to late August many of these plants exhibited 50-90% open boll. Thus, composited thermal imagery could serve as a useful alternative to vegetative indices (VI) in the prediction of early senescence promoted by heat/water stress in highly heterogeneous cotton fields, and facilitate development of site-specific application of defoliants/harvest aids.